Study On The Epitaxial Growth Technology Of The Nonpolar Ntype AlGaN Epi-layers

With the non-polar a-plane(11(?)0)Al Ga N material the quantum confinement Stark effect(QCSE)of the conventional c-plane polar Al Ga N along the material growth direction can be effectively eliminated,and theoretically the light emission efficiency of UV-LED can be effectively improved.In addition,the epitaxial growth of the non-polar Si-doped n-Al Ga N layer with high Al composition is critical for achieving the non-polar Al Ga N-based UVC-LED with high brightness and excellent performance.Therefore,the preparation of the non-polar Si-doped n-Al Ga N epitaxial layer with high Al composition is of great scientific significance and application value for the fabrication of Al Ga Nbased UV-LEDs with high external quantum efficiency.In this thesis,high quality non-polar a-plane(11(?)0)Al N templates and Al Ga N epitaxial layer were grown on semi-polar r-plane(2(?)04)sapphire substrates by using metal-organic chemical vapor deposition(MOCVD)technology.Moreover,the nonpolar a-plane(11(?)0)n-type Al Ga N material with high Al composition,outstanding crystalline quality,and superior surface morphology was achieved.This will pave the way to fabricate non-polar Al Ga Nbased DUV-LED with high efficiency.The major works conducted in this research are listed as follows:1)The high-quality non-polar a-plane(11(?)0)Al N template was successfully grown on the semipolar r-plane(2(?)04)sapphire substrate by using the three-step pulsed flow growth method.In fact,besides the remarkably reduced full width at half maximum values of both the symmetrical X-ray rocking curve and the A1(TO)Raman scattering peak,strong relative light transmittance and steep absorption edge were observed in the ultraviolet-visible absorption spectrum for the a-plane Al N template grown by the three-step pulsed flow growth method.Furthermore,a superior surface morphology and a decreased surface deformation were achieved with a root mean square(RMS)value as small as 3.4 nm in an atomic force microscope detection area of 5 × 5 mm2.2)The non-polar a-plane(11(?)0)Al Ga N thin films with various Al compositions were grown successfully on the r-plane(2(?)04)semi-polar sapphire substrates.The optical properties and thermo-optic effect of these films were studied extensively for the first time with angle-and temperature-dependent spectroscopic ellipsometry(SE).It was revealed that the non-polar Al Ga N has higher refractive index than its polar counterpart with the same Al composition.Moreover,it was demonstrated that the anisotropy for the non-polar Al Ga N thin film increased with increasing the Al composition.3)With the introduction of optimized two-way pulsed flow growth method technology,the nonpolar a-plane(11 (?) 0)Si-doped n-Al0.5Ga0.5N epi-layer was successfully grown.The characterization results revealed that the anisotropy in crystalline quality of the non-polar Sidoped n-Al Ga N epi-layers was suppressed effectively,and the surface morphology as well as the electrical properties including electron concentration(EC),electron mobility(EM),and electron resistivity(ER)had been significantly improved by using indium surfactant and inserting an extra Al Ga N buffer layer.In fact,an EC as high as 4.8×1017 cm-3,an EM up to 3.42 cm2/V·s,an ER down to 4.78 Ω ·cm,and a RMS value as small as 8.2 nm for surface roughness were achieved for the non-polar Si-doped n-Al Ga N with a relatively high Al composition of 50%.